====================================================== WARNING: possible circular locking dependency detected 6.16.0-syzkaller-06574-gd9104cec3e8f #0 Not tainted ------------------------------------------------------ syz.2.1295/10778 is trying to acquire lock: ffff8881427a05e8 (&q->elevator_lock){+.+.}-{4:4}, at: elevator_change+0xf0/0x320 block/elevator.c:677 but task is already holding lock: ffff8881427a00a8 (&q->q_usage_counter(io)#50){++++}-{0:0}, at: nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1478 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #3 (&q->q_usage_counter(io)#50){++++}-{0:0}: lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 blk_alloc_queue+0x538/0x620 block/blk-core.c:461 blk_mq_alloc_queue block/blk-mq.c:4400 [inline] __blk_mq_alloc_disk+0x15c/0x340 block/blk-mq.c:4447 nbd_dev_add+0x46c/0xae0 drivers/block/nbd.c:1943 nbd_init+0x168/0x1f0 drivers/block/nbd.c:2680 do_one_initcall+0x233/0x820 init/main.c:1269 do_initcall_level+0x104/0x190 init/main.c:1331 do_initcalls+0x59/0xa0 init/main.c:1347 kernel_init_freeable+0x334/0x4a0 init/main.c:1579 kernel_init+0x1d/0x1d0 init/main.c:1469 ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #2 (fs_reclaim){+.+.}-{0:0}: lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 __fs_reclaim_acquire mm/page_alloc.c:4045 [inline] fs_reclaim_acquire+0x72/0x100 mm/page_alloc.c:4059 might_alloc include/linux/sched/mm.h:318 [inline] prepare_alloc_pages+0x153/0x610 mm/page_alloc.c:4727 __alloc_frozen_pages_noprof+0x123/0x370 mm/page_alloc.c:4948 __alloc_pages_noprof+0xa/0x30 mm/page_alloc.c:4993 __alloc_pages_node_noprof include/linux/gfp.h:284 [inline] alloc_pages_node_noprof include/linux/gfp.h:311 [inline] pcpu_alloc_pages mm/percpu-vm.c:95 [inline] pcpu_populate_chunk+0x182/0xb30 mm/percpu-vm.c:285 pcpu_alloc_noprof+0xcbf/0x16b0 mm/percpu.c:1870 __alloc+0x80/0x180 kernel/bpf/memalloc.c:144 alloc_bulk+0x33b/0x530 kernel/bpf/memalloc.c:246 prefill_mem_cache kernel/bpf/memalloc.c:499 [inline] bpf_mem_alloc_init+0x45c/0xc60 kernel/bpf/memalloc.c:546 htab_map_alloc+0x8ec/0xc70 kernel/bpf/hashtab.c:575 map_create+0xaa3/0x1310 kernel/bpf/syscall.c:1477 __sys_bpf+0x60f/0x870 kernel/bpf/syscall.c:6004 __do_sys_bpf kernel/bpf/syscall.c:6132 [inline] __se_sys_bpf kernel/bpf/syscall.c:6130 [inline] __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:6130 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #1 (pcpu_alloc_mutex){+.+.}-{4:4}: lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 __mutex_lock_common kernel/locking/mutex.c:598 [inline] __mutex_lock+0x187/0x1340 kernel/locking/mutex.c:760 pcpu_alloc_noprof+0x286/0x16b0 mm/percpu.c:1782 init_alloc_hint lib/sbitmap.c:16 [inline] sbitmap_init_node+0x1e1/0x630 lib/sbitmap.c:126 sbitmap_queue_init_node+0x41/0x660 lib/sbitmap.c:438 bt_alloc block/blk-mq-tag.c:542 [inline] blk_mq_init_tags+0x110/0x280 block/blk-mq-tag.c:565 blk_mq_alloc_rq_map block/blk-mq.c:3542 [inline] blk_mq_alloc_map_and_rqs+0xbd/0x9f0 block/blk-mq.c:4098 blk_mq_sched_alloc_map_and_rqs block/blk-mq-sched.c:386 [inline] blk_mq_init_sched+0x28a/0x710 block/blk-mq-sched.c:485 elevator_switch+0x19c/0x5f0 block/elevator.c:595 elevator_change+0x21b/0x320 block/elevator.c:679 elevator_set_default+0x186/0x260 block/elevator.c:742 blk_register_queue+0x35d/0x400 block/blk-sysfs.c:905 __add_disk+0x677/0xd50 block/genhd.c:528 add_disk_fwnode+0xfc/0x480 block/genhd.c:597 add_disk include/linux/blkdev.h:773 [inline] nbd_dev_add+0x717/0xae0 drivers/block/nbd.c:1973 nbd_init+0x168/0x1f0 drivers/block/nbd.c:2680 do_one_initcall+0x233/0x820 init/main.c:1269 do_initcall_level+0x104/0x190 init/main.c:1331 do_initcalls+0x59/0xa0 init/main.c:1347 kernel_init_freeable+0x334/0x4a0 init/main.c:1579 kernel_init+0x1d/0x1d0 init/main.c:1469 ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #0 (&q->elevator_lock){+.+.}-{4:4}: check_prev_add kernel/locking/lockdep.c:3165 [inline] check_prevs_add kernel/locking/lockdep.c:3284 [inline] validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 __mutex_lock_common kernel/locking/mutex.c:598 [inline] __mutex_lock+0x187/0x1340 kernel/locking/mutex.c:760 elevator_change+0xf0/0x320 block/elevator.c:677 elevator_set_none+0x42/0xb0 block/elevator.c:757 blk_mq_elv_switch_none block/blk-mq.c:5022 [inline] __blk_mq_update_nr_hw_queues block/blk-mq.c:5063 [inline] blk_mq_update_nr_hw_queues+0x68f/0x1890 block/blk-mq.c:5113 nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1478 nbd_genl_connect+0x135b/0x18f0 drivers/block/nbd.c:2228 genl_family_rcv_msg_doit+0x215/0x300 net/netlink/genetlink.c:1115 genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline] genl_rcv_msg+0x60e/0x790 net/netlink/genetlink.c:1210 netlink_rcv_skb+0x205/0x470 net/netlink/af_netlink.c:2552 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline] netlink_unicast+0x82c/0x9e0 net/netlink/af_netlink.c:1346 netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896 sock_sendmsg_nosec net/socket.c:714 [inline] __sock_sendmsg+0x219/0x270 net/socket.c:729 ____sys_sendmsg+0x505/0x830 net/socket.c:2614 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2668 __sys_sendmsg net/socket.c:2700 [inline] __do_sys_sendmsg net/socket.c:2705 [inline] __se_sys_sendmsg net/socket.c:2703 [inline] __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2703 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f other info that might help us debug this: Chain exists of: &q->elevator_lock --> fs_reclaim --> &q->q_usage_counter(io)#50 Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&q->q_usage_counter(io)#50); lock(fs_reclaim); lock(&q->q_usage_counter(io)#50); lock(&q->elevator_lock); *** DEADLOCK *** 6 locks held by syz.2.1295/10778: #0: ffffffff8f56e3f0 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1218 #1: ffffffff8f56e208 (genl_mutex){+.+.}-{4:4}, at: genl_lock net/netlink/genetlink.c:35 [inline] #1: ffffffff8f56e208 (genl_mutex){+.+.}-{4:4}, at: genl_op_lock net/netlink/genetlink.c:60 [inline] #1: ffffffff8f56e208 (genl_mutex){+.+.}-{4:4}, at: genl_rcv_msg+0x10d/0x790 net/netlink/genetlink.c:1209 #2: ffff888142790988 (&set->update_nr_hwq_lock){++++}-{4:4}, at: blk_mq_update_nr_hw_queues+0xa6/0x1890 block/blk-mq.c:5111 #3: ffff8881427908d8 (&set->tag_list_lock){+.+.}-{4:4}, at: blk_mq_update_nr_hw_queues+0xb9/0x1890 block/blk-mq.c:5112 #4: ffff8881427a00a8 (&q->q_usage_counter(io)#50){++++}-{0:0}, at: nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1478 #5: ffff8881427a00e0 (&q->q_usage_counter(queue)#2){+.+.}-{0:0}, at: nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1478 stack backtrace: CPU: 0 UID: 0 PID: 10778 Comm: syz.2.1295 Not tainted 6.16.0-syzkaller-06574-gd9104cec3e8f #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025 Call Trace: dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2175 check_prev_add kernel/locking/lockdep.c:3165 [inline] check_prevs_add kernel/locking/lockdep.c:3284 [inline] validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 __mutex_lock_common kernel/locking/mutex.c:598 [inline] __mutex_lock+0x187/0x1340 kernel/locking/mutex.c:760 elevator_change+0xf0/0x320 block/elevator.c:677 elevator_set_none+0x42/0xb0 block/elevator.c:757 blk_mq_elv_switch_none block/blk-mq.c:5022 [inline] __blk_mq_update_nr_hw_queues block/blk-mq.c:5063 [inline] blk_mq_update_nr_hw_queues+0x68f/0x1890 block/blk-mq.c:5113 nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1478 nbd_genl_connect+0x135b/0x18f0 drivers/block/nbd.c:2228 genl_family_rcv_msg_doit+0x215/0x300 net/netlink/genetlink.c:1115 genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline] genl_rcv_msg+0x60e/0x790 net/netlink/genetlink.c:1210 netlink_rcv_skb+0x205/0x470 net/netlink/af_netlink.c:2552 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline] netlink_unicast+0x82c/0x9e0 net/netlink/af_netlink.c:1346 netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896 sock_sendmsg_nosec net/socket.c:714 [inline] __sock_sendmsg+0x219/0x270 net/socket.c:729 ____sys_sendmsg+0x505/0x830 net/socket.c:2614 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2668 __sys_sendmsg net/socket.c:2700 [inline] __do_sys_sendmsg net/socket.c:2705 [inline] __se_sys_sendmsg net/socket.c:2703 [inline] __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2703 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f1dbcd8eb69 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f1dbdb43038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: 00007f1dbcfb5fa0 RCX: 00007f1dbcd8eb69 RDX: 0000000020000000 RSI: 0000200000000380 RDI: 0000000000000005 RBP: 00007f1dbce11df1 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 0000000000000000 R14: 00007f1dbcfb5fa0 R15: 00007fff76c996e8 nbd1: detected capacity change from 0 to 127